In order to reduce the exposure of proton exchange membrane (PEM) fuel cells to problems resulting from freezing temperatures, and to reduce reliance on water pumps and other plumbing as accessories to the fuel cells, the total volume of coolant in the fuel cells may be reduced.
However, in systems which do not use either a coolant pump or a gas venting micropump, and have minimal external water plumbing, the flow rate of coolant in the cells is quite low. If only gas is vented from the coolant passageways, water flow is limited to that which evaporates into the reactant gases. With small passageways and low water flow, gas bubbles may join together (aggregate) and block water flow from large areas of the water channels, sometimes referred to as “gas breakthrough” of the reactant gas flow field plates, thereby causing localized heating and dehydration of the membrane at various spots, resulting in degradation of components and reduced performance.
Systems employing between-cell coolant plates, which have glycol or other coolants, may have extremely small, in-cell water passageways to provide low flows of water to the anode side of the fuel cells for hydration, with insignificant cooling resulting from the water flow.